The use of direct current (DC) electrical motor systems in vehicles is well known. For example, motor vehicles such as golf carts and personal mobility carts, having separate brake and throttle controls, utilized DC electrical motor systems with success. The relatively quiet operation of the DC electrical motor systems combined with their ease of use make them ideal for utilization in the motor vehicles.
Although the DC electrical motor systems have provided good overall performance in such motor vehicles, there have been difficulties in controlling the DC electrical motor systems in emergency situations. A particularly serious difficulty has arisen when the motor vehicle encountered a steep downhill slope.
In such an emergency situation, the operator was required to release the throttle control and activate the brake control. Unfortunately, the throttle and brake controls were susceptible to being mistaken for one another. As a result, a nervous operator was able to activate the throttle control and not the brake control under the emergency conditions, causing the motor vehicle to increase its downward momentum.
Even where the operator was able to distinguish between the throttle and brake controls, the operator had to have the presence of mind to deactivate the throttle control and activate the brake control. Where the throttle control and brake control were foot pedals, the operator had to be able to reach the brake pedal when the emergency arose. As the operator could be forced backward as the motor vehicle hurtled downhill, reaching the brake pedal was made difficult. As a result, the safety of the motor vehicle operator was at risk.
A DC electrical motor system for safely controlling motor performance of a motor vehicle was disclosed in U.S. Pat. No. 5,483,615. The DC electrical motor system included a DC motor having an armature winding and a field winding, wherein the armature current was electromagnetically coupled to the field winding current to facilitate controlling the magnitude of the field winding current relative to the magnitude of the armature current. By controlling the field winding current magnitude, the maximum rotational speed at which the DC motor developed motoring torque, i.e., the maximum motoring speed, could be controlled. Any increase in speed above the maximum motoring speed caused the DC motor to act as a generator, whereby an increase in rotational speed above the maximum motoring speed was resisted.
The disclosed DC electrical motor system further included a rotational speed control for determining the maximum rotational speed of the DC motor before it acted as a generator to develop a retarding torque. The rotational speed control enabled the motor vehicle operator to select one of a plurality of discrete settings corresponding to a similar number of maximum motoring speed settings. In this way, the operator was able to select a maximum motoring speed for the DC motor.
In one disclosed embodiment, the discrete settings were selected by a hand operated selector switch. In another embodiment, the discrete settings were selected according to the position of the brake control.
While the disclosed DC electrical motor system very satisfactorily enabled the operator to select the maximum motoring speed for the DC motor, the ability to select the maximum motoring speed by the vehicle operator was impaired during an emergency. In an emergency situation, the operator was subjected to a great deal of stress which affected the operator's decision making abilities. Selecting the appropriate maximum motoring speed during such an emergency required the operator to determine what selection was best suited for the situation, and to activate either the hand operated selector switch or the brake control, all in a very short period of time. As a result, the selection of the appropriate maximum motoring speed was difficult, especially for an inexperienced operator.
Therefore, it would be highly desirable to have a new and improved DC electrical motor system which provides a relatively fail safe way for controlling the maximum motoring speed of a motor vehicle.
During the operation of a motor vehicle, prior known DC electrical motor systems utilized the energy stored in battery cells, thereby decreasing the voltage stored by the battery cells. A continuing demand of current by the DC electrical motor systems while the voltage stored by the battery cells decreased had the potential for causing damage to the battery cells.
Therefore, it would also be highly desirable to have a new and improved DC electrical motor system that reduces the risk of damage to battery cells. Such a DC electrical motor system should be simplified in design and relatively inexpensive to manufacture.